Fluorescent spectroscopy is a well-known technique used to characterize test specimens which may be biological or chemical test specimens. In general, the technique consists of illuminating the test specimen with light of a known wavelength. Molecules of the specimen absorb the light and subsequently fluoresce, which is to say emit light having a wavelength different than that of the absorbed light. In particular, the wavelength of the emitted light is longer than that of the excitation wavelength (absorbed light).
The observed or detected emission spectra (light intensity as a function of wavelength), which is referred to as the fluorescence emission spectra, provides detailed information on the structure and bonding characteristics of the molecules of the test specimen. This information can be used, in turn, to characterize and identify the material(s) of the specimen with a high degree of specificity.
In at least one geometry disclosed in the prior art for fluorescence spectroscopy, the fluorescence emission spectrum is generated and measured by applying an electric field to the walls of a containing tube while the sample specimen is in the tube. Typically, the electric field is applied using a pair of electrodes in close proximity to the tube. With this particular approach, the optical excitation, and the emission detection, occur from the “side” of the tube, i.e. transverse to the applied electric field (and to the general length of the tube). There are, however, problems with this approach.
When applying an electric field to the “sides” of the tube, the maximum electric field that can be applied to the test specimen is restricted and limited by the width or diameter of the tube and the dielectric strength (one measure of which is the maximum breakdown voltage) of the material used for the tube walls. Even in those instances where it is possible to impart an electric field substantially parallel to the direction of illumination (through the use of transparent electrodes), the relatively small widths of the container tube restrict the volume of test material excited by the illumination. The sensitivity and accuracy of the test method/device are therefore significantly reduced by the limited volume of material illuminated/tested.
Further, with most if not all of the fluorescent spectroscopy test systems disclosed in the prior art, a single set of electrodes is used, and the electric field is often applied as a static, constant field. While adequate for many simple test needs and small sample volumes, these approaches do not provide the flexibility to vary the electric field either spatially, or as a function of time. Similarly, larger volumes of test material cannot be sampled and evaluated.
In yet another geometry found in the prior art, liquid samples are contained within a flexible tube that is in turn coiled about a structure, such as a cylinder, in which is placed a reflector. Light is presented transverse to the flexible tube so as to excite the samples within the tube. The reflector will reflect light passing through or between the coils of the flexible tube back towards the coiled flexible tube. Any resulting fluorescence induced within the liquid sample is transferred by an optical fiber to a remote spectrometer. Fluid flow through the flexible tube is generally required and the length of the tube must not exceed certain lengths.
In addition, as the fluid is excited in one location and the florescence of the fluid measured in at a physically separate and somewhat distant location, loss of florescence is an undeniable issue. Further, fluorescence, such as it may be found, is measured entirely from the blunt cross section end of the flexible tube which may be quite small.
Hence, there is a need for a fluorescent spectroscopy system that overcomes one or more of the drawbacks identified above.